A pair of complex tones is played four times against a background of noise. Do you hear the pitch go up or down?
Our auditory system has the ability to listen to complex sounds in different modes. When we listen analytically, we hear the different frequency components separately; when we listen synthetically or holistically, we focus on the whole sound and pay little attention to its components.
In this demonstration, which was originally described by Smoorenburg (1970), a two-tone complex of 800 and 1000 Hz is followed by one of 750 and 1000 Hz. If you listen analytically, you will hear one partial go down in pitch; if you listen synthetically you will hear the pitch of the missing fundamental go up in pitch (a major third, from 200 to 250 Hz).